Surface properties and wetting characteristics of leadfree solder alloys

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Surface properties and wetting characteristics of
lead-free solder alloys

• E. Ricci, D. Giuranno, F. Gnecco, S. Amore, T.
  Lanata, R. Novakovic
• National Research Council (CNR) Institute for
  Energetics and Interphases (IENI)
• Genoa - Italy

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Contribution from IENI Genova to COST 531
Characterization Surface Properties and wetting
behaviour of Selected groups of Lead-free Alloys
as Soldering Materials Surface Tension
modelling Binary systems Ag-Cu Au-Sn Cu
-Sn Au-In In-Sn Bi-In Wetting
behaviour Ternary systems Au-In-Sn/Cu Bi-In
-Sn/Cu Binary sub-systems Au-In/Cu Bi-In
/Cu Au-Sn/(Cu,Ni) In-Sn
/(Cu,Ni) Cu-Sn/(Cu,Ni)
Final Meeting COST Action 531 Vienna 17-18 May
2007
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Experimental
Preparation of the samples

• Preparation of the alloys from the pure elements
  by melting in a clean atmosphere
• Control of alloys compositions by SEM-EDS
• Mass of alloy sample mechanical and
  chemical cleaned

3.0 g ST measurements 1.0 g wetting experiments
Working Conditions
Surface Tension Measurements
Wetting Experiments

• Cu, Ni square plate (13x13x1mm)
  metallogrhaphically mirror polished (Ralt0.05
  mm)
• Ar N60 atmosphere PO2 10-6 Pa
• Texp Tl 50 K up to 900K

• Sapphire crucible
• Clean Conditions
• Flux Ar N60 atmosphere 10-4 lt PO2lt10-2 Pa
  Vacuum conditions Ptot 10 -5 Pa
• Tl 50 K ltTexplt 1300 K

Final Meeting COST Action 531 Vienna 17-18 May
2007
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Experimental
Temperature
Surface Tension
Oxygen Partial Pressure
Contact Angles
Acquisition of drop profile in real time (2 s) by
ASTRAview appropriate Software
g SV g LS g LV cos q
q gt 90 no wettability
q lt 90 wettability
Final Meeting COST Action 531 Vienna 17-18 May
2007
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Surface Tension Results
Final Meeting COST Action 531 Vienna 17-18 May
2007
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Surface tension
Au-In
Au-Sn
atAu
atAu
Experimental determination of the surface tension

Experimental data are in good agreement with
surface tension values calculated using different
theoretical models
Theoretical calculations of the surface tension
Final Meeting COST Action 531 Vienna 17-18 May
2007
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Surface tension
Bi-In
In-Sn
In
atIn
atIn
Bi
Experimental determination of the surface tension

Experimental data are in good agreement with
surface tension values calculated using different
theoretical models
Theoretical calculations of the surface tension
Final Meeting COST Action 531 Vienna 17-18 May
2007
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Surface tension
Cu-Sn
Ag-Cu
atCu
atCu
Experimental determination of the surface tension

T1373K 1 REG. SOL 2 Prasadsmodel ? Exp Results
Theoretical calculations of the surface tension
Final Meeting COST Action 531 Vienna 17-18 May
2007
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Wetting Results
Final Meeting COST Action 531 Vienna 17-18 May
2007
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Wetting Results
Final Meeting COST Action 531 Vienna 17-18 May
2007
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Interface Characterization
Cu substrate
h-Cu6Sn5 based phase
e-Cu3Sn based phase
In 70Sn

• Similar behaviour
• Cu-Sn/Ni
• Au-In-Sn/Cu

Ni substrate
Ni3Sn4 based phase

• As Pb-Sn solder alloys these systems show
• Formation of a layer (lt100 mm) of intermetallic
  compounds at the interface between solder alloys
  and substrate
• These reactions are dominated by the
  Sn-component, but the h and the e-phase are
  exchanged

? 14 mm
Final Meeting COST Action 531 Vienna 17-18 May
2007
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Interface Characterization
Excessive dissolutive wetting
Au-55In
Cu substrate
Erosion of the substrate and Increase in the
total volume of liquid phase
Negative influence on mechanical and electrical
properties

• Similar behaviour
• Cu-Sn/Cu

Final Meeting COST Action 531 Vienna 17-18 May
2007
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Interface Characterization
Bi-52In
Cu substrate
BiIn2
Cu
Interface macroscopically planar

• Similar behaviour
• Au-Sn/(Cu,Ni)
• Bi-In-Sn/Cu

Weakness of solder joint
Final Meeting COST Action 531 Vienna 17-18 May
2007
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Conclusions

• Complete characterization of the surface
  properties and the wetting behaviour of selected
  groups of lead-free solder alloys
• In-Sn and Cu-Sn are good candidates as basic
  systems for new lead free solders concerning
  their wettability on Cu and Ni
• The additional elements should be chosen in order
  to preserve the wetting properties to exchange
  the e and h phase formation at the interface, and
  inhibit the excessive growth of a reactive layer
  keeping good mechanical and electrical properties

Final Meeting COST Action 531 Vienna 17-18 May
2007
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Thank for your attention
Final Meeting COST Action 531 Vienna 17-18 May
2007